Recently, input devices using touch sensors, such as track pads, touch screens and the like, have become increasingly popular. In portable computing devices such as laptop computers, the input devices are commonly track pads (also known as touch pads). With a track pad, the movement of an input pointer (i.e., cursor) usually corresponds to the relative movements of the user's finger (or stylus) as the finger is moved along a surface of the track pad.
In the case of hand-held personal digital assistants (PDA) or mobile devices, the input devices tend to utilize touch-sensitive display screens. When using a touch screen, a user can make a selection on the display screen by pointing directly to objects on the screen using a stylus or finger. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel, or integrated with the panel, so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch event and the position of the touch event on the touch sensor panel, and the computing system can then interpret the touch event in accordance with the display appearing at the time of the touch event, and thereafter can perform one or more actions based on the touch event.
Touch sensor panels can generally be very thin, and can include a substrate with a thin patterned film laminated (or otherwise deposited or formed) thereon. However, due to the desired thinness of the substrate and thin film, difficulties can occur during fabrication due to the risk of damaging components of the touch sensor panel.
For example, when flexible substrates are processed by depositing the thin film, the transition temperature, at which point the substrate can warp or deform, may be relatively low. Generally, any processing of a flexible plastic substrate, for example, has to be below 150° C. or else it can deform. However, annealing the thin film at a high temperature (above 150° C.) is often desired, since it can improve the thin film's resistivity and optical properties. Hence, annealing the thin film while adhered to the flexible plastic substrate can cause an unwanted deformation in the substrate.